Fir Audio Krypton 5

Fir Audio Kr5 is the mid level of Fir's newest series called The New Frontiers. It uses a dedicated dynamic driver for the bass and four balanced armature drivers. It packs some great technologies, and it's priced at $2999.


Today we’ve got another IEM by the great company called Fir Audio. After reviewing their VxV, M5 custom, and XE6 custom, now it’s time for the Krypton 5, the so-called Kr5. 

This has been the most requested review ever on Ear Fidelity, with countless comments and private messages asking about comparing it to the XE6 and different IEMs. Well, you asked for it, and now it’s here.

The Fir M5 and XE6 forever changed my perception of IEMs. First, the previous flagship, the M5 has been a pleasure to own and use for over a year now, combining a great build quality and sound that was easy to fall in love with. Fall in love so much, that it actually has been THE IEM I took on my Caribbean vacation last year. The one and only, I didn’t need anything else, and they delivered.

Then, Fir Audio announced their new lineup, called The New Frontiers. Thanks to their generosity and faith in our reviews, I was lucky to get to choose one model to review. I went with the Xe6 in custom form, and boy oh boy. Ever since receiving them, these have been the best IEMs I’ve tried in my life. The best build quality on the market, perfect comfort, beautiful, rich, and romantic sound. To this day, this is my go-to IEM when I want some serious listening, traveling with me a lot, basically everywhere I go. I’ve been listening to music, working on video editing, checking audio levels while shooting and everything in between with them, and all I can say is that these are just absolutely marvelous.

However, a lot of you seemed hugely interested in a lower model, the Kr5. This could have been due to the price being more affordable, or you were following some reviews online, but seeing how requested these were, they drew my attention immediately. After all, the Xe6 should provide the best of the best of the new series, being a clear flagship experience, right?
Right, and they delivered it instantly. 

Audio is a fun hobby though, and the price doesn’t always follow rules. We’ve all seen flagships being beaten by lower models of the same manufacturers. Of course, the sound is highly subjective, so this will hugely depend on your liking, but the aspect of value can be evaluated rather objectively. 

I don’t want to spoil this review for you guys, so I’ll keep you on the edge of your seats for a little longer. Or, you can just fast forward to the summary and see how it went, this is totally up to you, but trust me, this will be a really fun review in my opinion. At least, a highly personal and emotional one. And when I get emotional in my reviews, you know that we’ve got something that will be praised a lot. 

Back to Fir Audio for a second. This is a company that really makes me smile. Their bunny logo, fun packaging, great, outgoing marketing, story-telling, etc. They haven’t been around for many years, but they surely earned their place as one of the best IEM manufacturers in the current high-end market. After owning the M5 and XE6, my expectations of their products grew significantly, especially since they entered the realm of really expensive products. Till now, everything Fir made has been worth its high price for me, will the Kr5 be the same? Let’s dig into it.


The unboxing experience has been a strong point of Fir Audio products, and it’s no different this time. Actually, these sport the same packaging as the Xe6, but I’m going to get into it anyway. 

The IEMs come in a hard box with a graphic sleeve. Fir Audio has really mastered its design and graphic game, so the Sleeve simply looks stunning and modest at the same time. Not too flashy, but not default at the same time. I’ve been doing story-telling for an IEM company years ago as my job, and I know how hard it is to create something unique and non-cliche. Because of that, I enjoy that little aspect, even more, seeing how coherent the whole branding has been for Fir Audio.

Okay, let’s get inside. There’s not a lot happening inside, as you’re getting the IEMs with the cable, a great, round, leather case, and an absolutely stunning badge. Again, this is what makes me excited, just look at this thing. I’m still trying to figure out how to use it, as I’m a freaking minimalist, but I’m pretty desperate to saw it on something and wear it with pride, it’s just so cool.

That’s not all though, as you’re getting some goodies in the leather case as well. Before that, let’s discuss the case itself though. It is made of leather, has that bunny logo on top, and the closing mechanism is just brilliant. It’s just snug and secure, so even though there’s no zip or clasp, you don’t have to worry that it’ll open on its own. Actually, I’ve been tossing this thing a lot in my camera backpack, suitcase, etc, and it just never failed. Such a great little thing, and because it’s leather, it’s pretty lightweight, so you can also put it in the pocket of your jacket and not feel like you’re carrying an anvil in your pocket. 

I said it in my Xe6 review, and I’ll say it again. This is highly subjective, but I wish that they stayed with that beautiful burgundy case color that they used for their M5, it’s just such a beauty. I get it, black is black, and black is universal, but still, I just had to write it.

Inside the case, you’ll get a cleaning brush, some eartips (just ignore these), and a set of Atom modules. Yes, the universal Fir Audio IEMs also come with that fantastic thing, and it’s bonkers. Atom modules have been game changers for me, and I’m happy to see that they’re present here as well.

I said ignore the eartips, because if you’re spending $3000 on a pair of IEMs, you probably have a full arsenal of different eartips that you like. Just go with your Comply, Final E-Type, Xelastecs, Symbio, or whatever tickles your fancy. Yes, it would have been cool if Fir Audio included some of these in the box, but it’s also okay that they haven’t. These are cheap and widely available, just order some and try them for yourself. My go-to eartips are Comply and AZLA Xelastecs. 

Overall, the unboxing experience of the Kr5 is pretty Fir Audio-like. Nothing really epic or ultra-luxurious, but well thought-out and just great, stylish, and useful. You just simply can’t feel disappointed. 

Design, Build and Comfort

Okay, my experience with Fir Audio for the past year and a half was Custom IEM only. This is refreshing, and actually very interesting to see and rate the build of their new models.

First of all, these IEMs are way smaller and lighter than you think they are. When I first saw the new lineup in the photos, I immediately had a feeling that these are huge and heavy. When I took the Kr5 out of the box for the first time, I was bamboozled. These IEMs are small, not too heavy, but they feel like a tank. 

So, the actual quality of the build is just perfect. Fir Audio is making outstanding CIEMs when it comes to their physical aspect, and the new universal models are just as good. They feel very substantial, rigid, and insanely strong in the hand, I wouldn’t be scared by even dropping them from like two meters, these shells aren’t going anywhere. 

Every single edge is made to perfection, everything feels smooth and again…perfect. I tend to critique the build of IEMs from time to time, but I truly have nothing to say here. As far as the overall design and shape of these go, this couldn’t have been done better. Kudos!

Now, onto the design. This is highly subjective, but I really like the way these look. The sapphire crystal faceplates with carbon fiber infused in them are just hypnotizing. Yes, they are not screaming at you like “LOOK, I COST AS MUCH AS SOME CARS”, but I don’t feel like it was intended by Fir Audio. This is polished, mature, yet interesting and just classy. The only “big” thing about these are the nozzles, as these are really thicc. Don’t worry, you won’t have any problems with installing your eartips (can’t say the same about uninstalling some!), so this is not a problem. 

This has a pro though – remember the old times when nozzles on IEMs could break or become crooked? Well, as long as you’re not hulk, these won’t do that…ever.

Lastly, the Kr5 (and all the new models actually) now use 2-pin connectors, instead of MMCX that you could find in the previous models. This gives me mixed feelings. I know people dislike MMCX connectors, saying that they are unreliable and they break easily. Funny, because my experience with IEMs was perfectly opposite in the past. I never had an MMCX connector fail, and 2-pin…well, I won’t say the same. However, people tend to like 2-pin a lot more, so who am I to judge it? If people prefer 2-pin, Fir Audio has made a good choice. The 2-pin sockets found on the Kr5 are actually replaceable, so if they actually ever break…you’re covered, and this is a great, great thing. 

Since we’re talking build, let’s get to the cable as well. The one included with the Kr5 is…okay. Nothing extraordinary, nothing bad, it’s decently comfortable, doesn’t tangle, it sounds okay, it works okay, what can I say? Again, these are $3000, you’ll probably cable roll them (oh my and you should, but more on that later!), so the included cable shouldn’t really be your concern. If you won’t cable roll them though, this cable is good enough to just forget about it. Just use it, it won’t break, it won’t annoy you, that’s everything you should expect from it. 

When ordering, you can choose the termination of your cable, which is a great thing to have. Nowadays, most of you will opt for a 4.4mm termination anyway, but it’s great to have a choice. I actually went with a 3.5mm one, to use them with my XIAudio Broadway S. Well, not only because of that, I just got so many 2-pin, 4.4mm cables that they’ll easily last me a lifetime, so I decided to go with a 3.5mm. It’s easier to use with my camera, Macbook, and other devices that only have a 3.5mm output, so I don’t have to remember to pack my 4.4mm to 3.5mm DDhifi adapter. Of course, most critical listening has been done with a 4.4mm cable, as it should have been.


Fir Audio has some really interesting technologies up their sleeves, so let’s discuss the ones used in the Kr5, and there are quite a few of them. 

First of all, the most important one is the Kinetic Bass. This is a game changer for the entire IEM industry, and I really mean it. See, for many, many years you had bass that you can hear, better or worse, but that was the whole story. I actually have a lot of experience with stereo setups as well, and I always missed that thumbing effect on my body when listening to some bassy recordings.

It all has changed by Unique Melody, which was the first company to implement bone conduction technology into IEMs, and this was just so relieving. Finally, a bass that you can not only hear but also feel!

UM has improved its BC technology since the original MEST, but Fir Audio went a step further. The Kr5 uses a vent on the inner side of the shells, so this driver blasts right at your ear, creating a simply spectacular feeling of the most tactile and physical bass that you’re going to find in the IEM hobby, but more on that in the sound paragraph, let’s leave the goodies till then.

The second technology is Atom Venting. You’re probably already familiar with it, but I’m going to quickly explain what it is about. Basically, it’s a pressure relief system that vents the air pressure that builds up inside the shells. This has two goals – to let you listen to your IEMs longer without fatigue and to actually tune the sound signature to your liking, by simply changing the ATOM modules, that you’re getting included in the box. 

Then we’ve got the Open Acoustics. Most IEMs use sound tubes, that carry the sound wave from the driver directly to the nozzle. Fir Audio found a solution to leave the drivers without sound tubes, and they say that it results in a much bigger sound with a bigger soundstage. While it’s hard to truly evaluate this one, we just have to believe them and judge all of this by our listening tests.

Lastly, the Rigid Technologies. This is a proprietary technology that provides industry-leading durability and serviceability to Fir Audio’s IEMs. Remember when I said that the 2-pin connectors are replaceable? Exactly that. 

Oh, one last thing, the Atom Modules. As I covered them previously, I won’t go too deep into them this time. You can read all the necessary information here.

These will basically let you change the amount of isolation of your IEMs, slightly altering the sound. You’re getting three different modules with the Kr5: Silver, Black, and Gold. Silver is the most neutral one, black has 2db less isolation, and gold has 2db more isolation than silver. Take note that this review was done using mainly the silver module, as this sounds just perfect for me. You will get slightly more bass response with gold modules, and a slightly airier, thinner sound with the black ones. 

Atom modules have always been a neat feature in Fir Audio products, and it is a great way to fine-tune your new IEMs to your liking. The difference in the sound is not huge, it’s subtle, allowing you to slightly alter the tuning. However, the stock silver ones, that are originally installed in the Kr5 are just ideal in my opinion, and they do offer the most natural sound.


Paweł, are you writing a book? All those words and you haven’t touched the sound yet!

Well, well, I told you, this is an emotional one. Okay, it’s time to say about the most important aspect, the sound. Till now, I was trying to remain pretty calm and informative, but now it’ll all change. 

You see, I’ve been in this hobby for over 10 years now. I have worked in the audio industry for years, I’ve been doing marketing, sales, distribution, production, I ran an ultra high-end audio store, etc, etc. All of this experience in my life made me try A LOT of different audio devices, often ones that cost as much as a new sport Audi. I’ve built stereo systems costing hundreds of thousands of dollars, I’ve listened to most high-end headphones ever created, and I’ve been to many places and done many things. As a reviewer, I tend to be as objective as I can, but sometimes it’s really hard.

Actually, you really rarely see me writing negative reviews of audio gear. I’ve been wondering lately, and I found the reason. You see, I’ve been selling audio for a living for many years in the past (not any more of course), so I have mastered the job of understanding different people’s opinions and preferences. Not everyone likes the same sound signature or qualities of audio products, people are different, they hear different, they feel different and there are very few really BAD audio products in my opinion. Let’s take an X product, for example, you tried it and you think it’s absolutely horrible, right? Well, the company sold thousands of those and people really enjoy it. They tried it, bought it and they use it for years now with pleasure. Who is right in this equation? Well, no one is actually. People treat music so emotionally, and as I said, we’re all different, that it’s impossible to truly understand who likes what when it comes to the sound. 

There has been a massive outbreak of audio objectivists in the past few years, and they are behaving like they are going to save the world from filthy audio manufacturers that scam people left and right. Well, this is much more complicated than this. Yes, the frequency graph is important, the measurements are important, and all of this is really important for audio. I’m not trying to discourage you guys from listening to these guys. My reviews are on a subjective side of the spectrum, I never tried to hide it, because my experience in audio got me to this place when I believe that this is the way I want to do things. 

However, the measurement is one thing, and people’s preferences are another. And I’m not only talking about frequency response preferences. You’d be surprised if you were to work in an IEM store and see how complicated people are with sound. I just want to say it out loud – stop acting like the frequency response is everything there is to audio because it isn’t. It would have been if we were all measuring devices, but we aren’t. We are people, we have emotions, tastes, and moods and we are often unreasonable, and that’s beautiful about it. 

You can see a lot of people lately that have never tried a specific IEM, but they claim it’s absolutely horrible, and they back it up with a frequency response graph. Listen up, good audio is not only the “neutral” audio, and there’s more in life than just perfect Harman. If audio products have been manufactured for robots that all hear and like the same, it would have been fair. But it isn’t. People have their own idea of the “perfect sound”, and it’s often nothing even close to being 100% tonally accurate.

Audiophiles usually don’t even want a flat, accurate response in their headphones/IEMs/speakers. They want a little boost here and there, a little dip here and there, they want a sound that is specific, that has something interesting in it, that sounds a specific way. 

That’s what bugs me with audio objectivists lately. You guys are doing incredibly important work, you push the manufacturers into making objectively more “accurate” and higher fidelity audio products, and that’s wonderful. However, the way you guys attack everyone in the hobby and call people names because “ooooh you’re such a noob, change hobby, this frequency response literally says that this product is trash and it should be boycotted” is just beyond me.

Stop acting as if you are an audio Messiah, because you are not, and you never will be. Treat people with respect, and get to understand that people are people, and they do like different things, even if they are sometimes “objectively worse”.  What’s worse and better in audio anyway? Is faithfully reproducing the material better? With literally zero coloration? For measurements, it definitely is. But there are people that actually listen to stuff and music, and they do get emotional by these, rather than simply reading the graph. If you only care about the measurements, just don’t buy any IEMs, print the best measuring IEM’s graph and hang it on the wall above your bed. I’m sorry, but it often seems like the only thing you guys care about.

So yeah, no frequency graph in this review, no measurements (not that I don’t believe in them), simply a subjective, emotional take on the sound of an audio product. Feels like good old 2010, doesn’t it?

Okay, fun, but you still haven’t told us a word about the sound of the Kr5, what’s up with that emotional message above?! It has its purpose, as I just want you guys to understand my point of view. 

Why? Well, because this review is going to be absolutely weird in a way. I told you that I’ve tried A LOT of different audio devices in my life, and I’m going to say it out loud and confidently – the Fir Kr5 is the best I’ve heard in my life. Now we can get going.

The bass, oh my god. In the TECH paragraph, I stated that the Kinetic Bass technology will change the IEMs industry forever, and I’m standing by my word. Forget about everything you’ve heard with traditional drivers, this is just a different world.
First of all, the texture, speed, decay, control, and richness of the bass are just absolutely spectacular. This is an ultra snappy, ultra-detailed, and insanely controlled bass performance, that does everything fantastically. It doesn’t matter if you’re listening to electronic music, rock, jazz, acoustics, or some crazy-ass binaural audiophile recordings. The Kr5 does all of these with authority, yet it sounds so natural and detailed that it almost sounds unreal.
Now, here comes the fun part, the physical aspect of the bass of this IEM is just like nothing else in the world, except the XE6. When you’ll hear some hard-hitting bass notes in the recording, you’ll actually feel them physically, which is an absolutely weird, but pleasant and engaging feeling. These IEMs can hit as hard as it gets, creating that insane tactility you could only feel in live music or some crazy stereo setups with high-end subwoofers. Well, not anymore. 
And it’s not about that huge, big physical slam. This is just a part of it. What’s the most impressive is how real and physical different instruments and sound effects sound. You can have a kick drum that sounds like it’s just there, or a male vocalist with such body to his voice that you can actually feel the air he exhales. This is just so multi-dimensional, that it’s actually hard to explain, without you experiencing it. 
For years now, I have a feeling that the over-ear headphones market is absurdly bass-light. I had a lot of customers that never went into headphones, simply because they couldn’t have felt the bass. This is where good IEMs come in and totally change their perspective, and the New Frontiers series by Fir Audio are going to do it even more successfully. This incredible bass performance made me listen to the Kr5 more than to my Susvara, simply because in comparison, the Hifiman flagship just can’t compete in the bass department, it’s not even close. Yes, comparing the IEMs and over-ear planar headphones is a little dumb…or is it?
Back to the Kr5 though. Let’s put that bass in the perspective. The last studio album of Tool, called Fear Inoculum has a pretty mental song on it, called Chocolate Chip Trip. It’s all about Danny Carey AKA the Octopus and his insane drum kit, doing some weird magic. This song sounds so insane on the Kr5 that it’s beyond explanation. Every single hit of the drumsticks, every single piece of air moved by the snare drum, the kick drum, and the tactile feeling of the entire drum kit is just ridiculous. Get the Kr5, play this song and close your eyes, and you’ll be feeling like this drum kit is placed around your head and Danny just smashes as hard as he can. This is beyond audio quality, this sounds just real, like you’re there. 
Let’s give you one more example. There’s an artist called RY X, who does some pretty nostalgic, sad and melancholic music, which I’m a huge sucker for. He just launched a new album, called Blood Moon, and the first song of this album is a single, called Let You Go. It starts with two acoustic guitars playing on both sides of your head, then the vocal comes in, and then…the beat. I never realized how powerful this beat is before trying it on the Kr5, this just changes this song completely for me. It actually feels like every other IEM I tried this song on has failed to reproduce it properly, it’s that impressive. Marvelous. 

Now, let’s get to the midrange, and here things start being complicated for me. I know, that as a reviewer, I really shouldn’t be saying it, but I tried, I really pushed myself to think differently, to change my mind, but I failed, so I’m going to say it – for me, the midrange is literally perfect. 
I’ve compared the Kr5 to many IEMs, my over-ear headphones, to some high-end speakers, everything I was able to, and this is just the best there is. First of all, let’s get the technical stuff out of the way. The Kr5 is the most detailed IEM I’ve heard, and it’s not subtle. The amount of little details these little things can blast to your ear canals is absolutely sick. I have some test songs and albums that I tried over years and years in this industry on many setups, including stereo systems that cost as much as a new Bentley, and yet I found new micro-details with the Kr5. They just simply deliver an astonishing amount of details so effortlessly, so elegant and natural. The Kr5 is much more detailed than the XE6, and the XE6 is really detailed, to begin with. 
Secondly, the resolution, and here it becomes mental. I’m just going to explain it in my own way. Let’s use our eyes for a second. You see, find an 8K screen, play the most insane native 8k material on it, and tell me what you see. The image becomes so insanely sharp, that you can clearly see the edges of a single hair of an animal. Do you see it as sharp in real life? Probably not. Does that mean that 8K material and an 8K screen have more resolution than real life? Hell no.
What’s the deal then? I see it that way: real life is so sharp, the resolution of our eyes is so high, that it gets so sharp, that it’s not sharp anymore. Sounds weird? Yeah, probably, but think about it. Everything natural that you see, your hand for example. You see it as perfectly clear and sharp as it’s possible, but it doesn’t look sharp, it just looks organic, like there’s no edge. There’s not even the tiniest line between your arm and the background, it’s just so sharp, that it’s not sharp anymore, it just looks the way it should.
This little weird comparison has its purpose in this review, don’t worry. You see, this is exactly how I feel with the Kr5. The resolution of this IEM is so high, so crisp…that it doesn’t sound sharp or crisp, like not even the slightest. We’ve all tried some ultra-technical sounding audio gear that just made everything sound artificial, unpleasant, fake. The Kr5 has the technical performance at an absolute godlike tier, but it’s just natural, smooth, real sounding. 
Take a song called Abraham, by Miles Mosley. There’s some serious bass action in this song, and with the Kr5 you’ll be getting a lot of string action, I mean A LOT of string action. Every single string vibrating, smashing into each other, moving air around it. You’re getting even the tiniest details of it, but it never sounds firm in a bad way. It sounds firm, because the tactile bass doing its job perfectly, but it still manages to sound incredibly natural and lifelike. 
Vocals are another story, as I’m yet to find a single one that doesn’t sound absolutely marvelous on the Kr5. David Gilmour, Mariusz Duda, Lana Del Rey, Melody Gardot, Sam Smith….all of them sound just real, incredibly natural, engaging. The Kr5 has that magical touch of warmth to its midrange, where everything sounds just pleasant, natural, and harmonic, but it’s also as accurate as it gets. This is BY FAR the best midrange I’ve heard in an IEM.

The treble, oh the treble. First of all, something that came into my mind as the first thing when listening to the Kr5 for the first time. I’ve never ever heard an audio product having so much treble, while not being sharp like…whatsoever. There’s just literally no sharpness to it, no, nada, null. Yet, it’s just so incredibly detailed, clean, shimmering, and forward sounding when it should.
To truly understand this, I must go back to the whole “8K screen” narrative from the midrange section. The Kr5 has such a tremendous amount of resolution, that it’s just impossible for it to sound sharp. You’re simply going to hear every little treble detail, every single shimmer, but it’ll never feel forced, unnatural. Have you ever stood next to a drum kit in a music store and just randomly smashed that cymbal with a drum stick? Been there, done that. These things sound so much different than most music recordings reproduce. They have that weight to their sound, that richness, together with a slight ringing effect that is just utterly uncomfortably pleasant, but never painful. This is exactly what the treble of the Kr5 sounds like. On the edge, extreme, in your face when it should, but never ever unpleasant or fake. It’s so rich, that you’ll start to enjoy the treble a lot more. A lot of people tend to EQ the treble of their affordable audio down, as it just can’t handle that amount of information and it starts sounding harsh and tiring. With the Kr5, you never have to worry about it, just blast your favorite album and enjoy it as it should be enjoyed. 
This leads us to another absurd thing about the Kr5. This thing just makes everything sound good. Yes, an IEM as detailed with such an outstanding resolution sounds great with poor mastering. It truly does. 
The more detailed gear people get, the more demanding the choice of music becomes for the most part. You’re starting to see how badly mastered your favorite album is, and it simply becomes painful to listen to. We all experienced it at some point in our audio journey. This is why the Kr5 is truly a gem, as it just makes everything sound great. I’ve been trying some really poorly mastered albums with them, the ones that should put the audio engineer involved in prison for the crime he committed. Guess what? I ended up just listening to the whole thing, rediscovering new details and enjoying that mind-boggling timbre, having a lot of fun with a recording that is literally unlistenable on most of my high-end gear. This is some serious witchcraft from Fir Audio. I actually e-mailed them about the Kr5, asking “what sorcery is this”, but they seem to not understand my question – well, who can blame them, I’m just a maniac that found something he’s been waiting for for years. 

Let’s get to the soundstage now. Fir Audio claims, that thanks to its “Open Acoustics” system, their IEMs offer a bigger and more expansive soundstage. While it’s impossible to evaluate the truth behind that statement, we can just simply describe staging capabilities of the Kr5. So, this is once again, breathtaking. The soundstage is incredibly wide, deep and accurate, with fantastic height and separation. Once again, the Kr5 has an outstanding separation which further improves the accuracy and separation of every single sound coming into your ears. Additionally, that tactility provided by the Kinetic Bass technology makes every instrument stand out even more, giving you a soundstage that is not only huge and accurate, but also marvelously natural feeling. 
One of my benchmark tracks for rating the soundstage is Dusk by Edison’s Children, a side project of Marillion’s bassist Pete Trewavas. This track has so much ambient atmosphere in it, it’s full of air, distant yet forward, it’s just an incredible song, I highly recommend checking it out. Back to the soundstage though, there’s a lot of playing with distance in this track, vocals getting right in front of you, just to slowly float away into the distance, and it’s really great to check the capabilities of IEMs. The Kr5 handles this song like a champ, creating a highly atmospheric, accurate soundstage that just slowly hipnotize you. Once again, this is just incredible.

To summary the sound section of this review – the Kr5 just sounds like a perfect IEM to me personally. Remember, that this is my subjective evaluation and I’m just telling you what I’m personally feeling. However, out of every single IEMs and headphones I’ve ever tried, this is definitely the closest one to sounding truly lifelike. The scale of technical superiority combined with an incredibly rich and accurate tone and an insane doze of fun in it, makes it my absolute all-time favorite, beating the Xe6 by quite a margin actually (more on that in the comparison section). 

For me, audio has always been about emotions. We’ve got a lot of audio objectivists nowadays, but I’m more old-school, as I think that every single person has a different taste, they’re used to different sound type and they have their own, individual “sound goal”. It’s just a huge pleasure for me to review this IEM, as I’ve never ever felt so close to finding that perfection in audio, and I have listened to quite a lot of different audio devices. The Fir Kr5 is truly a special one for me, and while this review has been absurdly positive, I’m just giving the credit where it’s due. This is my subjective rating, and I’m saying it out loud: This is the best IEM/Headphone in the world for me. Of course, I haven’t heard everything there is, and I’m yet to try some of others TOTL IEMs such as the Vision Ears EXT, Traillii, Jomo Audio stuff, etc. But out of everything I tried so far, this is it. 



Final A8000

The Final Audio A8000 has always been known for its fantastic technical performance and tuning that surely wasn’t for everybody. That Beryllium Dynamic Driver has been a marvel for years already, and the A8000 has found a lot of owners, even though it comes at a rather hefty price tag ($2000).

The IEM market is constantly evolging though, so this is very interesting to compare the Kr5 to an IEM that has set the bar back in 2019.

As far as the overall presentation, unboxing experience and build quality go, I’d say that these two trade blows. Both are great, but they do deliver different kinds of emotions. The A8000 is of course, more “Japanese” in a way where everything is incredibly coherent and just pure quality. The unboxing experience, while not very luxurious, is just elegant and mature. The Kr5 on the other hand, is more fun and modern, lacking that aspect of elegance and refinement.

When it comes to the build quality, both are exceptional. The A8000 definitely looks more interesting with their polished Stainless Steel shells that just look absolutely lovely. However, I never managed to listen to them for more than two hours straight, as sharp edges of the shells start making me uncomfortable. A 10 minute break is all it takes, but still, for me this is a bit of form above function. The Kr5 on the other hand, while not looking as impressive, is more comfortable. The biggest problem of the A8000 for me is the nozzle lenght, and it’s a lot longer in the Kr5, resulting in a more secure, comfortable fit for me personally. 

Let’s get to the sound. Starting from the bass, the A8000 has absolutely nothing to say when compared to the Kr5. As I already said a couple of times, the Kinetic Bass technology is a game changer, and the Kr5 just wipes the floor with the A8000 when it comes to the bass. After listening to the Kr5 for a few hours, you put the A8000 in your ears and you just immidiately feel underwhelmed by its traditional bass reproduction. There’s no tactility, no physicality, no rumble. The midrange is somewhat a similar story, where the Kr5 feels more natural, full-bodied and more tactile, with better detail retrieval. The A8000 definitely sounds brighter, firmer and more aggressive, where the Kr5 is just right in the middle, sounding incredibly natural. The treble feels similar at first, but the amount of resolution of the Kr5 is superior to that of the A8000, giving you a much more pronounced yet smoother and more realistic treble presentation. As far as the soundstage goes, the A8000 is a great IEM, but the Kr5 goes a step further. This part isn’t as dramatic as the previous ones, but still, the Kr5 comes out as a better choice.

The A8000 has had a wonderful run for these past three years, and I still have friends that rock these as their daily driver, with no desire for a change. However, the price difference between the two is not that huge (if you can spend $2000 on a pair of IEMs, you can probably spend $3000 as well), and seeing how much better the Kr5 sounds in every aspect, it’s definitely, unmistakely worth paying extra.

Dita Perpetua

We have just reviewed the new Perpetua flagship IEM by Dita, really enjoying its unique tuning and a very coherent sound signature that is just perfect for chilling. Since the price tag of both the Perpetua and the Kr5 is the same, it would have been a pity if we haven’t compared the two, so here it goes.

Let’s start with the unboxing experience. The Perpetua is just something else in this regard, offering a much better, more generous and luxurious feeling presentation than the Kr5. There’s absolutely no doubt who’s the winner here.

As far as the build quality goes, the Perpetua uses Titanium shells with an elegant and down-to-earth design. However, these IEMs are just humongous when compared to a way more compact Kr5. This hugely reflects on the comfort, since I can wear the Kr5 for longer periods of time. The Perpetua is by no means an uncomfortable IEM for me, but the Kr5 is just more comfortable. Additionally, this might just be be, but I somehow feel that the Kr5 is more robust and will survive a more hardcore abuse than the Perpetua (please don’t test it).

Let’s get to the sound. These two IEMs have a similar capability of sounding incredibly pleasing and coherent, but the Kr5 is just a much more technically impressive IEM out of the two. The detail retrieval and resolution of the Kr5 are miles ahead of those of Perpetua, sounding more insightful and way more detailed. The biggest strength of the Perpetua is its tuning which makes everything sound relaxing and pleasing, but the Kr5 takes it to another dimension. 

Using five drivers instead of one, implementing a few ground-breaking technologies such as Kinetic Bass, Open Acoustics, Atom Venting, etc makes for a much more impressive and technical sounding IEM that sets the new standard for the industry. While the Perpetua is a really good, unique sounding IEM that will fill a niche for some people, the Kr5 is just a force to be reckoned with for every single IEM in the world. We’re talking about very good vs the best. 

Fir Audio XE6
Here’s something that a lot of you have been waiting for. Usually, an audio manufacturer reserves the “flagship” slot in their lineup for the absolute best product they make. Ever since I got the Xe6, I immediately fell in love with them, claiming that they are my new favorite IEMs of all time. Well, they haven’t held that status for too long.
And what a surprise it is that actually, a lower model of the same manufacturer took that nr.1 spot for me. Let’s dive in.
Speaking about the unboxing experience, these two are just almost identical, so I don’t want to waste your time. The build quality is also impossible to rate, as the Xe6 I’ve got is a custom version, whereas the Kr5 is universal. Both are built exceptionally well, so at least I can give you that.

Now onto the sound. The Xe6 is an absolutely awesome pair of IEMs, definitely one of the most intense and fun sounding that I’ve ever heard. However, there are a lot of differences between the Xe6 and the Kr5.

First of all, the Xe6 has an even bigger and even more physical bass than the Kr5. One could actually argue which one is simply “better” in the bass, but I think that this will come down to personal preferences. The bass of the Kr5 is slightly quicker, leaner and a bit more textured. The Xe6 however offers an unrivaled intensity, rumble, and physicality to low frequencies. Some users have actually pointed out that the Xe6 has bigger Kinetic Bass openings, which may lead to a bigger bass presentation, but it’s just a guess.

Here the slight similarities end. The Xe6 is definitely more colored, more intense sounding and actually, it’s also sharper. The Xe6 is probably still the most fun-sounding IEMs on the market with its ridiculous bass response, fantastic richness and smoothness to the midrange, and forward and splashy-sounding treble. The Kr5 however just sounds more natural, coherent, and mature, not being as extreme, but it just sounds more lifelike.

What’s most surprising though, is that the Kr5 is even more detailed, and it offers a higher resolution than the Xe6. Yes, two aspects that are almost always reserved for flagship models, are going to a lower, less expensive model. This situation for me looks a little like a “secret weapon” of Fir Audio, as I actually believe that the Kr5 is a better IEM overall, not even mentioning that it’s more “affordable”. Of course, if you’re after a more unique, crazy fun, and intense-sounding IEM, the Xe6 is still a fantastic job and I’ll keep recommending them left and right, but if you want the “best of the best”, the Kr5 is your guy. 
One more thing, as a reviewer, I have a great possibility to watch brands grow and improve, and Fir Audio is just a beautiful story. When I was reviewing their VxV back in early 2021, I stated that this company has the potential to really shake up the audio market, they weren’t quite there yet, but they surely were going in the right direction. Now we’re in mid-2022, and Fir Audio is now sitting on the very top of the audio mountain, being one of the best, if not THE best IEM manufacturers in the world in my opinion. This is what hard work, an innovative mind, and bravery get you. It’s a huge pleasure for me the be observing this from a front row, and I’m keeping my fingers crossed for Fir Audio for the future. Who knows what they will come up with in the future, and if they’ll keep improving, and will release an IEM that is even better than the Kr5, then I don’t know if I’m prepared for that. Luckily, it’ll take some time till we get there.
Fir Audio M5
This direct comparison will tell us how much of an improvement Fir Audio has made over the last year. The M5 is a flagship model of their previous M-series lineup, with a price of $2799.

As you can see, the previous flagship is actually less expensive than the current “mid” model, but all of this RnD doesn’t come cheap. 

Once again, I’m not going to compare the unboxing experience, as not a lot has changed honestly, mainly the case. The same goes for the build quality, as once again, my M5 is custom, and the Kr5 I’ve got is universal. 

That leads us straight to the sound quality. This might sound harsh, but the reality is simple: The Kr5 is a much, much better sounding IEM than the M5, in every single way. First of all, the Kinetic Bass makes the bass response of the Kr5 miles ahead of the one found in the M5, this is not even a competition, it’s a slaughter. Everything else, while not being AS dramatic, is still very significant as well. The detail retrieval, resolution, coherency, soundstage, and timbre are all way better on the Kr5, which just feels like a completely different, more mature and technically impressive product.
The Fir M5 is by no means a mediocre IEM, I still use it quite frequently to this day and I enjoy it a lot. This is just an aspect of comparing a very good IEM to a God-Tier one, you just simply cannot argue the superiority of the Kr5. Once again, this is exceptional how much Fir Audio improved its products over the last year or two. Having in mind that these cost more or less the same amount of money, I cannot find a single reason why you should go with the M5 over the Kr5. New models, lineups, and technologies are not always better when it comes to audio, but in this specific situation, it’s just a big, big difference.
Hifiman Susvara
Okay, let’s get really serious. Let’s compare the Kr5 to the best pair of open-back, planar-magnetic headphones in the world, the almighty Susvara.
While comparing IEMs to full-size headphones might not sound too logical, both are meant to reproduce the sound, so even though their form factor is vastly different, the core aspect remains the same.
So, to truly understand my impressions of the Susvara, you should go and read our “Battle Of The Flagships” article here. The Susvara has secured an nr.1 spot in our big comparison, and for a reason. For me, this is the best pair of headphones you can buy right now, regardless of the price.
The Fir Audio Kr5 actually reminds me of a “compact” Susvara a lot, with one major difference – the bass. I cannot praise the Kinetic Bass enough, and I’m going to do it again. When compared to the Kr5, Susvara just sounds lean and boring in the bass department, lacking that tactility and physicality. Of course, not every single one of you will want to have that kind of bass response, but once you’ll try it…there’s no going back.
As far as the rest of the sound is concerned, these two are actually quite similar. Both offer unparalleled detail retrieval and resolution, both are incredibly natural, sweet, and engaging sounding, while not sounding harsh or artificially “good”. This is Peak Audio, where everything just sounds incredibly right, coherent, and insanely lifelike. If you own the Susvara and you always wanted to bring that level of sound quality out of your cozy home, you can just now. The Kr5 is an IEM version of the Susvara with an addition of a godlike bass performance (think about the Susvara with 1266’s bass), and you can put it into your pocket, while not needing a nuclear reactor in your backpack to power them properly. 


I’m going to do something I’ve never done in my reviews before. While listening and testing the Kr5, I tried them with a couple of different aftermarket cables, which have given me slightly different results, so I want to share my experience with you. At the end of the day, you might pull the trigger on the Kr5 and wonder what upgrade cable to get, so maybe this will help you.


Our “Best Cable of 2021”, the Erua Tawa remains in my arsenal as one of the go-to cables to pair with high-end IEMs. Its incredibly rich midrange and great separation prove to improve almost every single IEM I try it with significantly.

When paired with the Kr5, it adds a little of that “magical mist” to the midrange, resulting in a slightly more calm and romantic sound. The overall sound becomes more organic and sweet while keeping that insane technical capability. Definitely a great pairing if you want a slightly less neutral type of sound, with a focus on color, richness, and sweetness. I really enjoy this one during my late-night listening sessions, when I really want to chill and relax. Definitely a big step-up from the stock cable.

Astral Acoustics Eclipse

This cable is more of a “safe” option for the Kr5. It makes them sound a little warmer, it adds body to the sound and makes the treble a little less energetic. I will call the Tawa a better pairing in this specific example, as the Kr5 doesn’t really need that extra body and warmth. 

However, if you own a rather technical or slightly harsh-sounding system, the treble of the Kr5 might come up as a touch too much for you, hence the Eclipse might be a great choice in this situation. If your system is good and neutral/natural though, I’d rather go with the TAWA personally.

Cross Lambda Apollo GB

The review of this cable is currently being written, but oh what a review this will be. Let me start by saying, that this cable costs $6000, which is just absurdly a lot for an IEM cable. The customers and sales will eventually evaluate if this price is anything near being “reasonable”, but for now, this comes as a huge shock for everyone.

Let’s not focus on the price though, as honestly, I’ve seen speaker cables costing as much as $100k, so $6000 for an IEM cable doesn’t look that insane for me personally. At the end of the day, there are some really wealthy people walking around us, that make that amount of money in an hour. If a person buys it and enjoys it, is it really that absurd? Nope.

Okay, the sound. Apollo GB is a cable that offers a Godlike black background and separation, and the overall tone of it is very natural and neutral. This pairs with the Kr5 just insanely good, as it just lets the Kr5 show its whole capability. The resolution, detail retrieval, texture, and control just sound incredible, like I’ve never heard before. While I won’t go as far as recommending you to buy a $6000 cable for a $3000 pair of IEMs (this would have been mental), I can definitely say that this pairing just sounds heavenly. This just proves to me, that the best cable you can pair the Kr5 with, is as neutral and technically capable as possible. You don’t really need to alter the sound signature of the Kr5, just give it the best “objectively” sounding cable and let it spread its wings. 


If you made it this far, you already know how incredibly in love I am with this IEM. Good unboxing experience, perfect build quality, and the best sound I’ve ever heard, not only from a pair of IEMs, but from any audio product ever. All of these give me no choice, and I’m officially crowning these as my subjective “Best IEMs in the world”. 

The search for the perfect sound is a journey that takes years. I’ve been into audio for 10 years already, listening to stuff that costs as much as a new Bentley, and after having the Kr5 for a while now, I’ve never felt that close to the goal of finding “the perfect sound”. 

This review was highly emotional for me and it probably was a bit chaotic and weird for you to read, and I apologize. However, I tried my best to focus on the aspect of enjoyment, as truly great audio is not only about great measurements and natural tuning, there’s more to it. A truly great audio product brings emotions, and the Kr5 did that for me like nothing ever before. 

It is my huge pleasure to recommend the Kr5 to everyone that has $3000 to spend, as you surely won’t feel disappointed. This is THE IEM to get right now. 

Fir Audio – Fantastic job, whatever sorcery you put into these, it works. Can’t wait for your next releases. I will definitely have my fingers crossed.

Gear used during this review for the sake of comparison and as an accompanying equipment:

  • Headphones – Fir Audio Xe6, Fir Audio M5, Final A8000, Dita Perpetua, Campfire Audio Supermoon, Unique Melody MEST, MEXT, Hifiman Susvara, Meze Elite, Final D8000 Pro, Sony MDR-Z1R
  • Sources– Cayin N3Pro, Hifiman EF400, EarMen Angel, EarMen Tradutto, Yulong Aurora, LittleDot MK III SE, SMSL SH-9, SMSL DO100 + HO100, FiiO M11 Plus ESS, XIAudio Broadway S, Burson Playmate 2, XIAudio K-DAC, Hiby RS6, Burson Playmate 2

Big thanks to Fir Audio for providing the Krypton 5 for this review. I wasn’t paid or asked to say anything good or bad about this product, all of the above is just my personal, unbiased opinion. Fir Audio hasn’t seen this review before publishing it.